Backup systems for solar water heaters (mainly with panels larger than 2 m2 of capture area) are used in high hot water demand systems or in processes where a constant hot water supply is necessary. Although there exist auxiliary water heating systems such as those cited in PCT Patent Applications Nos. WO/2007/101899; WO/2007/053859; WO/2007/000112; WO/2005/061969; WO/2005/040695; WO/2005/026627; WO/2004/038305; WO/2002/084037; WO/1998/004874; WO/1996/018072; WO/1995/004905; WO/1982/003271; and WO/1981/002774, the aforementioned references focus mainly on systems related to electricity and lack backup support from another type of energy.
On the other hand, solar water heaters with panels of less then 2 m2 of capture area typically use, as backup systems to avoid lack of hot water, traditional water heaters connected to the top part of the solar panel storage tank, additionally obtaining variable energy savings. This is in contrast to the water heater of the present invention.